This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-055524, filed Feb. 28, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention generally relates to a liquid crystal display panel which uses both transmission light and reflection light to display an image, and more particularly to a liquid crystal display in which each pixel comprises a static memory or the like for storing display data.
2. Description of the Related Art
Conventionally, mobile communication terminals, including portable phones and pagers, employ a display panel capable of displaying a simple character image of numerals and letters. In general, the display panel for this purpose has the properties of compact size, light weight, thinness, and low power consumption. With the remarkable progress in information technology, the capability of displaying a high-resolution color graphic image is also demanded for the display panel.
A reflection-type active matrix liquid crystal display panel is regarded as a promising type of display panel that can satisfy the demand described, and has been put into practical use in some kinds of mobile communication terminals. Such a liquid crystal display panel has a configuration in which an image is displayed by reflecting external light and optically modulating it, and thus requires no internal light source. With this configuration, a fine pixel structure can be achieved without restrictions being imposed by the need to allow transmission of light from an internal light source. Meanwhile, a problem arises in that visibility of the displayed image decreases significantly in the dark as compared with outdoors in daylight.
The above-mentioned problem can be remedied without requiring any modification to the pixel structure by means of a front light system having a transparent surface light source disposed on the front side of the display screen, for example. In this case, the surface light source serves as a subsidiary internal light source which compensates for a shortage of illumination provided by the external light. The front light system, however, requires a precise patterning process of transparent resin in order to uniformly deliver light from the surface light source to all the pixels, thus increasing the cost. As for the quality of the image, a decrease in the brightness, blurring of the image, an increase in image depth, etc., occur since the image is displayed with the reflection light transmitted through the transparent resin.
Jpn. Pat. Appln. KOKAI Publication No. 11-316382 discloses a liquid crystal display panel that uses both transmission light and reflection light to display an image. As shown in FIG. 8, in the display panel, each pixel includes a reflection area RA for reflecting external light and a transmission area TA for transmitting light emitted from a backlight unit BL. The reflection area RA is obtained by a pixel electrode RE of a metallic material, while the transmission area TA is obtained by a transparent pixel electrode TE of ITO which is formed within an opening provided as a void space surrounded by the pixel electrode RE. In a bright environment, such as outdoors in daylight, an image is displayed with the reflection light from the pixel electrode RE. On the other hand, in a dark environment, such as at night, an image is displayed with not only the reflection light reflected from the pixel electrode RE but also the transmission light transmitted through the transparent pixel electrode TE. It should be noted that the backlight unit BL is provided as a subsidiary internal light source which supplements a shortage of illumination provided by the external light, and the structure of the display panel tends to be restricted by the requirements for transmission of the light from the backlight unit BL.
The SRAM (Static Random Access Memory) technology is conventionally known as means for reducing the power consumption in a liquid crystal display panel for the mobile communication terminal. With this SRAM technology, each pixel has a wiring structure providing a static memory which stores display data supplied from a driving circuit via a polysilicon thin film transistor. For example, when a still image is displayed, update of the display data is not required. Accordingly, after the static memory has stored the display data from the driving circuit, the output operation of the driving circuit can be suspended so as to reduce the power consumption.
Memory wirings are formed of a light-shielding metallic material like signal lines XL, scanning lines YL, and wirings for thin film transistors SW for pixels, which are formed together with the memory wirings in a polysilicon TFT process recently put into a practical use. The area of the memory wirings occupies a large part of the pixel. Thus, when the transmission area TA is provided as a single and large window located at the center of the pixel, the memory wirings shield part of the transmission light to be transmitted through the transparent pixel electrode TE, and cause the effective transmission area to be significantly reduced in comparison with the area of the transparent pixel electrode TE. For this reason, an increase in the brightness of the backlight unit BL is required for attaining an image of a desired brightness, and this inevitably increases the power consumed by the liquid crystal display panel. This problem makes it difficult for the SRAM technology to be applied to the liquid crystal display panel that uses both reflection light and transmission light.
The present invention has been made in consideration of the above problems, and an object of the invention is to provide a liquid crystal display panel which can prevent the light use efficiency from being decreased due to light-shielding memory wirings applied to a display system that uses both reflection light and transmission light.
The present invention provides a liquid crystal display panel which comprises light-transmitting first and second electrode substrates, and a liquid crystal layer held between the first and second electrode substrates and containing liquid crystal molecules whose alignment is controlled from the first and second electrode substrates. The first electrode substrate includes an electrode which applies an electric field to the liquid crystal layer; a thin film transistor formed as a switching element for the electrode; a light-shielding wiring pattern having a plurality of memory wiring layers connected to the electrode and the thin film transistor, and one or more apertures which allow transmission of light from a rear side of the first electrode substrate; and a reflection member which reflects incident light applied from a second electrode substrate side through the liquid crystal layer, and overlaps the light-shielding wiring pattern such that the one or more apertures are left unmasked.
In the liquid crystal display panel of the present invention, the reflection member overlaps the light-shielding wiring pattern such that the one or more apertures are left unmasked. In this case, a decrease in the light use efficiency can be prevented by determining the layout of the light-shielding wiring pattern so as not to adversely affect the effective transmission area for the transmission light.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.